[enricher] Add gitlabcomments Enricher

[vchrombie]

Work on adding gitlabcomments enricher to get a better understanding of how enrichers work in ELK.

[vchrombie]

The gitlab enricher enriches the data of issues and merge requests just like how github enricher works for issues and pull requests. Later, github2 was introduced which enriches the review data like the issue comments, and emoji reactions. The idea is to create a similar enricher for gitlab too.

Here is the initial discussion, chaoss/grimoirelab#208.

[vchrombie]

Working branch 👉 https://github.com/vchrombie/grimoirelab-elk/tree/gitlabcomments.

[vchrombie]

Pull Request 👉 chaoss/grimoirelab-elk#881.

• enricher
• configurations
• schema
• tests

review pending ⏳

[vchrombie]

chaoss/grimoirelab-elk#881